► The traditional approach to damp inter-area oscillations is through the installation of Power System Stabilizers (PSSs) which provide damping control action through excitation control systems…
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▼ The traditional approach to damp inter-area oscillations is through the installation of Power System Stabilizers (PSSs) which provide damping control action through excitation control systems of the generating units. However, study of recent blackouts has shown that the control action provided by a PSS alone is not sufficient for damping oscillations in modern power systems which operate under stressed conditions. An integrated form of control using remote measurements to coordinate the different control elements present in the system is the need of the hour.
One way of implementing such a coordinated control is through the development of a Linear Matrix Inequality (LMI)-based polytopic model of the system that guarantees pole placement for a variety of operating conditions. The size of the polytopic formulation is an issue for application of LMIs to large systems. The use of SelectiveModalAnalysis (SMA) alleviates this problem by reducing the size of the system. The previous attempts have used a model containing all the and modes, with SMA being used to eliminate all the other states. In practical applications the resulting system was still found to be too large to use in a polytopic model. This thesis presents an algorithm to reduce the size of the system to the relevant modes of oscillations.
A 16 machine, 68 bus equivalent model of the New England-New York interconnected power system is used as the test case with DC lines and SVCs acting as the control. The algorithm is then applied to a 127-bus equivalent model of the WECC System. The use of ESDs as a form of control is also demonstrated. The results indicate that the proposed control successfully damps the relevant modes of oscillations without negatively damping the other modes. The control is then transferred to a more detailed 4000+ bus model of the WECC system to realize its performance on real-world systems.
Advisors/Committee Members: Thorp, James S. (committeechair), Centeno, Virgilio A. (committee member), Broadwater, Robert P. (committee member).

Spinal muscular atrophy (SMA) is a neurodegenerative disease characterized by motor neuron loss and skeletal muscle atrophy. In human the loss of function of the smn1 gene, the main supplier of survival motor neuron protein (SMN), leads to reduced levels of SMN and eventually to SMA. The anuran amphibian Xenopus tropicalis is a good animal model for the study of SMA and motor neurons development. Indeed the inhibition of the production of SMN using antisense morpholinos leads to caudal muscular atrophy in tadpoles. To develop an inheritable SMA model, we edited the smn gene in X. tropicalis using zinc-finger nucleases (ZFNs) and CRISPR/Cas system. As a first step, we designed the molecular tools needed to induce mutations of the smn gene using ZFN and CRISPR/cas9. Next we probed the efficiency of these tools and developed a method to identify mutations using T7EI and Surveyor endonucleases. We obtained a mutant frog and thus we will be able to produce homozygous mutant embryos for smn. In parallel we developed a transgenic line of Xenopus tropicalis frogs in which we can image motor neurons populations in vivo. The combination of both lines should enable to increase our knowledge and understanding of motor neuron physiopathology due to smn mutations.

► The manifestation of radiation and stored energy by electric currents on conducting bodies is studied via modal expansions. The novel modal expansions are based on…
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▼ The manifestation of radiation and stored energy by electric currents on conducting bodies is studied via modal expansions. The novel modal expansions are based on the quadratic operators which map a current distribution to each quantity. Adaptations of the continuous forms of these operators into the Method of Moments is reviewed. The discrete modal expansions are studied on several example objects, leading to conclusions regarding the sparsity of the radiation mode spectrum. Analytic forms for the sparse radiation modes on electrically small objects are derived. Negative energy current distributions are studied using the energy storage modal expansions. The role of ground plane radiation on the determination of an embedded antenna's Q factor is studied using radiation modes, giving a new perspective on the convergence behavior of this parameter with respect to ground plane size. Leveraging the invariance of radiation modes on small objects, an example procedure for the design of an embedded antenna array using radiation modes is presented.
Advisors/Committee Members: Bernhard, Jennifer T (advisor), Bernhard, Jennifer T (Committee Chair), Jin, Jianming (committee member), Gong, Songbin (committee member), Franke, Steven J (committee member).

Traditional modal parameter identification usually require measurements of both the input force and the resulting response in laboratory conditions. However, when modal properties are to be identified from large structures in operation, usually the possibilities to control and measure the loading on the structure is rather limited. In this case, the modal testing is usually performed using response data only. Operational ModalAnalysis (OMA) or Operational Modal Testing is a method where no artificial excitation needs to be applied to the structure or force signals to be measured. In this case, the modal parameters estimation is based upon the response signals, thereby minimizing the work of preparation for the test. However, standard OMA techniques, such as NExT, are limited to the case when excitation to the system is a white stationary noise. The NexT assumes that the correlation functions are similar to the impulse response functions, and then, traditional time domain identification methods can be applied. However,…

► Impact hammer is the current modal testing way in Dynapac testing department. Due to highly damped characteristic of big construction machines, there are a…
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▼ Impact hammer is the current modal testing way in Dynapac testing department. Due to highly damped characteristic of big construction machines, there are a few weaknesses for modal testing when using hammer, such as short response time, limited frequency resolution, poor quality of frequency response functions. Therefore, a more advanced excitation equipment is needed to improve the measurement quality. The object for this study is to compare two different measuring methods. The thesis will show a comparison between the hammer testing and the shaker MIMO testing compared with analytical model in a highly damped system. It will also give a reference for further highly damped modalanalysis and budgetary assessment to decide the budget expenditure. Result from shaker testing shows a little better correlation than hammer testing compared with FEM model. While the correlation between FEM model and measurement is bad due to many reasons, such as many local modes that can not excited, lack of excitation points, unexpected noise and error from the measurement. While considering the compared results obtained from this machine for now, a simpler structure experiment is suggested to be carried on in the future. Shorter length of stinger can be used to enable higher amplitude of force to excite the property on this machine.

► In this modern developing world finite element model is one of the main tools and they are becoming more and more advanced day by…
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▼ In this modern developing world finite element model is one of the main tools and they are becoming more and more advanced day by day in all mechanical fields. Before manufacturing a product the demands for finite element model is more between the manufacturers. The finite element method is considered as a powerful technique which is developed for solving the numerical solution of the complex problems in structural mechanics. In welded frame finite element modeling, finite element method is used and in for comparing the results, and its corresponding behavior, co-relation with the use of experimental modalanalysis. Experimental modalanalysis is nothing but a simple non-mathematical presentation. This thesis involves both analytical as well as experimental measurements. By means of using modal theory, analytical model is created so as to resemble the experimental data. The welded frame measurements are taken from college lab and the readings are observed by use of experimental modalanalysis. The result of this thesis work includes updated model of the frame which is experimentally taken into consideration and there measurements are both analytically and experimentally co related. Here the initial finite element model of the welded frame showed a bit differences when compared to experimental data. There are four beams that are being investigated and compared with the experimental data. An acceptable error was secured for natural frequencies when compared with experimental results and with the updated version of finite element model.

These research works presented in this manuscript aim at designing, simulate, manufacture and characterizing the modal converter based microstructured air-silica cane. This function represents a key element for modal multiplexers and chromatic dispersion compensators. The proposed component is based on a tapered microstructured air-silica cane « taper » which constitutes a transition between the two different fibers. The conversion is done through the excitation of a particular mode in a multimode or few mode fibers from a standard fiber. In the tapered structures, the understanding of the different theories involving the coupling between the different modes was yet necessary. A thorough study is carried to analyze the phenomenon of coupling and study the adiabatic criterion. This component is developed around an existing manufacturing technology at XLIM which based in the technique « stack and draw». Finally, we validate numerically and experimentally that principle. We succeed to excite the fundamental mode and higher order modes in a multimode fiber.

► The classic Stroop task, during which one names the ink color of color words, has long been used as a measure of selective attention (Stroop,…
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▼ The classic Stroop task, during which one names the ink color of color words, has long been used as a measure of selective attention (Stroop, 1935). Selective attention generally refers to our ability to attend to one stimulus (a target) while ignoring another (a distractor). Since its initial creation, many variations of the classic Stroop task have been developed. One of these variations is cross-modal Stroop, which uses visual colored targets and auditory distractor color words. However, whether the same mechanisms and processes are used while completing the two tasks has yet to be determined. The following thesis examined cross-modal Stroop and the theories that have been developed in an attempt to explain the classic Stroop findings. Two experiments were conducted. In Experiment 1, different colored visual stimuli were used (e.g. color squares and @ symbols) to determine whether this had any impact on task performance. A row of X’s induced significantly less interference, suggesting that they serve as an excellent neutral stimulus. In Experiment 2, the response times and accuracy levels for repeating auditory color words and visual colored items were examined with or without accompanying distractors. Although the classic Stroop task displays a very clear asymmetry between word reading and color naming, this asymmetry was not found for cross-modal Stroop. This finding suggests that the same processes and mechanisms may not be involved when completing cross-modal Stroop as classic Stroop, and furthermore, that some of the theories are better at explaining the cross-modal Stroop effect than others.

Lutfi-Proctor, D. A. (2013). An examination of the stimuli used in and the theories behind the cross-modal Stroop task. (Masters Thesis). Louisiana State University. Retrieved from etd-06252013-120151 ; https://digitalcommons.lsu.edu/gradschool_theses/3784

Lutfi-Proctor, Danielle A. “An examination of the stimuli used in and the theories behind the cross-modal Stroop task.” 2013. Web. 25 May 2019.

Vancouver:

Lutfi-Proctor DA. An examination of the stimuli used in and the theories behind the cross-modal Stroop task. [Internet] [Masters thesis]. Louisiana State University; 2013. [cited 2019 May 25].
Available from: etd-06252013-120151 ; https://digitalcommons.lsu.edu/gradschool_theses/3784.

Council of Science Editors:

Lutfi-Proctor DA. An examination of the stimuli used in and the theories behind the cross-modal Stroop task. [Masters Thesis]. Louisiana State University; 2013. Available from: etd-06252013-120151 ; https://digitalcommons.lsu.edu/gradschool_theses/3784

► n this paper presented a simple structural system synthesized from modalanalysis results. A method for determining the eigenvalues of a synthesized system by using…
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▼ n this paper presented a simple structural system synthesized from modalanalysis
results. A method for determining the eigenvalues of a synthesized system by using the
frequency response function (FRF). This method first used matrix Auto-Regressive
Moving Average (ARMA) model in the Laplace domain to describe each subsystem.
Then a modal force method by ARMA model could be established. Only the FRF at the
connecting joints is needed in the analysis to form a matrix named modal force matrix
(FRF matrix). From this matrix, both synthesized system modes and substructure modes
could be extracted simultaneously. Since the inverse operation is not required to form
modal force matrix, the computation is reduced drastically. The eigensolution of the
system in any frequency range could be determined independently.
ANSYS and MATLAB software’s used to extract the modal parameters of synthesized
structural system and each subsystem separately from this matrix (modal force matrix).
Finally compared their results.
Advisors/Committee Members: Dr. A. Raman (advisor).

► Operational ModalAnalysis has received a great deal of recent research and industry interest. This method has gained popularity due to potential for reduced test…
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▼ Operational ModalAnalysis has received a great deal
of recent research and industry interest. This method has gained
popularity due to potential for reduced test time and cost as well
as application to large-scale structures where traditional modalanalysis is difficult or impossible. Operational modalanalysis has
been shown to provide natural frequency and mode shape estimates
that are equivalent to those delivered through traditional modalanalysis. However, the damping estimates from the technique are
often inaccurate. This investigation focuses on the damping
estimates delivered by traditional modal parameter estimation
techniques when using output only data. Theoretical cases involving
5 degree-of-freedom and 15 degree-of-freedom systems are examined.
Investigations into the effect of system damping and rank
deficiency are also examined.
Advisors/Committee Members: Allemang, Randall (Committee Chair).

► The goal of this project is to learn the necessary steps to create a finite element model, which can accurately predict the dynamic response…
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▼ The goal of this project is to learn the necessary steps to create a finite element model, which can accurately predict the dynamic response of a Kohler Engines Heavy Duty Air Cleaner (HDAC). This air cleaner is composed of three glass reinforced plastic components and two air filters. Several uncertainties arose in the finite element (FE) model due to the HDAC’s component material properties and assembly conditions. To help understand and mitigate these uncertainties, analytical and experimental modal models were created concurrently to perform a model correlation and calibration. Over the course of the project simple and practical methods were found for future FE model creation. Similarly, an experimental method for the optimal acquisition of experimental modal data was arrived upon. After the model correlation and calibration was performed a validation experiment was used to confirm the FE models predictive capabilities.
Advisors/Committee Members: Charles D. Van Karsen.

► Methods of inferring excitation forces from measured accelerometer data have received significant attention in recent years. This thesis attempts to combine existing techniques with force…
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▼ Methods of inferring excitation forces from measured
accelerometer data have received significant attention in recent
years. This thesis attempts to combine existing techniques with
force gauges to determine excitation forces on a vibrating
structure. A mathematical algorithm was derived and applied to
theoretical and experimental data where a known impact force was
applied to a plate mounted through force gauges. These experiments
were used both to validate the mathematical algorithm and to
investigate its limitations. The results show that the applied
force for a fixed structure can be reconstructed better than force
gauges alone using a combination of force gauge data and free
boundary condition modalanalysis. Additional results demonstrate
that this method is capable of rejecting unwanted external forces
that were applied to the main structure.

This thesis presents a procedure for the development and validation of a theoretical vibration model, applies this procedure to a pair of aircraft engine casings,…
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▼

This thesis presents a procedure for the development and validation of a theoretical vibration
model, applies this procedure to a pair of aircraft engine casings, and compares select
parameters from experimental testing of those casings to those from a theoretical model using
the Modal Assurance Criterion (MAC) and linear regression coefficients. A novel method of
determining the optimal MAC between axisymmetric results is developed and employed.
It is concluded that the dynamic finite element models developed as part of this
research are fully capable of modelling the modal parameters within the frequency range of
interest. Confidence intervals calculated in this research for correlation coefficients provide
important information regarding the reliability of predictions, and it is recommended that
these intervals be calculated for all comparable coefficients. The procedure outlined for
aligning mode shapes around an axis of symmetry proved useful, and the results are
promising for the development of further optimization techniques.

► The sound radiated during a tennis impact has been shown to greatly influence the perception of 'feel' but has also been suggested to contribute to…
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▼ The sound radiated during a tennis impact has been shown to greatly influence the perception of 'feel' but has also been suggested to contribute to the perception of equipment quality, as is the case with many other consumer products. In an industry that is governed by design limitations, tennis racket manufactures are continually aiming to differentiate their products from their competitors' and the sound character of a racket is seen as one such method to do so. In order to control the sound radiated from a tennis racket it was first necessary to identify how a tennis racket radiates sound. Through a number of controlled player tests, involving groundstrokes and serves, the sound was recorded along with measurements of the physical vibrations excited in the frame. Analysis of the data revealed typical characteristics of the sound in the time and frequency domain. The sound was split into two sections to aid the analysis; an initial impulsive component that decayed very quickly and a ringing component that was of much lower amplitude but decayed at a much slower rate. The evolution of the frequency content over time was also investigated, however, the data provided much more information as to where each frequency component originated by analysing the data together with the experimental modalanalysis data. The experimental modalanalysis of a tennis racket was a vital stage in understanding which components of the racket were responsible for radiating the identified frequency component in the sound spectrum. The investigations identified frame bending modes, out-of-plane and inplane, as well as torsional modes, hoop modes and stringbed modes. To enable direct comparison between the natural frequencies excited during a tennis shot and the frequencies recorded from a freely suspended racket, the effect of the hand on the modal behaviour of the racket was analysed; experimental modalanalysis data from a hand-gripped racket was compared with data generated by adding simulated mass to the modal model of the freely suspended racket. The first stringbed mode was identified as a key contributor to the sound of the racket, especially in the ringing component of the sound. Analysis of the physical vibrations in the frame following a tennis shot revealed that the first stringbed mode excited the frame of the racket, which is iv thought to be the reason why stringbed modes contribute to the sound more so than their surface area would suggest that they are capable of. Analysis of the relationship between subjective perceptions of players and calculated sound metrics suggest a negative correlation exists between the duration and loudness of a tennis shot and the appeal of the sound. Further investigations involving a jury to evaluate the appeal of a tennis impact sound, modified in terms of duration, revealed further evidence to support the theory that tennis impact sounds of greater duration are less appealing than those that decay quickly. This is the first study to investigate the sound radiated from a tennis racket and has…

► In this thesis, the dynamics of two plates overlapping and connected by three bolts are studied. The data collected in the test are used…
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▼ In this thesis, the dynamics of two plates overlapping and connected by three bolts are studied. The data collected in the test are used in modalanalysis. The vibrational test and the modalanalysis were made using an LMS system. Hammer excitation is used for the tests. The main purpose of this thesis is to study how the suspensions affect the extracted eigenfrequencies and modal dampings. In this thesis, more than 10 suspensions were examined. Another objective in this thesis work is to build an FE-model. This model is made using the software Abaqus. To improve the reliability of the FE-model, a set of reliable experimental data is used to calibrate the model. The calibrated FE-model, using the measurement data, has a dynamic behavior close to the measurement data.

► This thesis starts from the construction of a mathematical model of the multi-segment mooring line, based on the work-energy variational method. The equations of motion…
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▼ This thesis starts from the construction of a mathematical model of the multi-segment mooring line, based on the work-energy variational method. The equations of motion in both Cartesian and Lagrange local coordinate systems are derived. Meanwhile, with the catenary theory applied, the static equilibrium configuration of the multi-segment mooring line is determined. Furthermore, Galerkin?s finite element method is used to generate mass, stiffness and damping coefficient matrices of a single mooring line. The coefficient matrices in the Lagrange local coordinate system are shown to be diagonal, which means the motions in the three directions of this coordinate system are uncoupled. With this information, the eigenvalue problem is solved to obtain the natural frequencies and associated mode shapes of a mooring line in both coordinate systems. By approximating the mooring line as a linear system, the modal superposition approach allows computationally efficient modeling of dynamics in the frequency domain, including estimation of extreme value statistics using Rice?s theory for Gaussian processes. The accuracy of the modal superposition approach is demonstrated through comparison with results from nonlinear time domain simulations using OrcaFlex. This approximate modeling approach is useful for optimizing the design of a mooring system in the preliminary phases of design.
Advisors/Committee Members: Mercier, Richard S (advisor), Chen, Hamn-Ching (committee member), Xie, Zhizhang (committee member).

►Modalanalysis is a critical part of the automotive development process. Identification of the vehicle's modal signature, especially in the low-frequency end of the spectrum,…
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▼Modalanalysis is a critical part of the automotive
development process. Identification of the vehicle's modal
signature, especially in the low-frequency end of the spectrum, is
essential for tuning the dynamic performance of the vehicle
structure for optimal ride and handling comfort. Traditional
methods to characterize the system - in terms of its natural
frequencies, associated damping values and mode shapes - have
typically employed conventional impact and shaker tests. While
these tests are able to accurately study the modal behavior of the
vehicle under static conditions, they are not truly reflective of
the real-world operating conditions of the vehicle A four-post road
simulator is used in automotive development to simulate on-road
conditions in the laboratory primarily for durability,
transmissibility, noise and vibration studies, etc. Some of these
studies often involve a similar setup of response sensors across
the automotive structure as conventional modal tests. Utilization
of the road-simulator for modalanalysis can potentially reduce the
duration of the automotive development cycle in the testing phase,
allowing for a faster time-to-market, in addition to improved
accuracy of estimation of the vehicle's dynamic performance under
simulated operating conditions. This thesis work explores the
feasibility of using a four-post road simulator for experimental
modalanalysis (EMA) of automotive structures. The MTS 320 Road
Simulator in the Structural Dynamics Research Laboratory,
University of Cincinnati, is employed for the study, with a truck
frame being the test structure. Frequency response functions (FRFs)
are estimated with displacement and pressure measurements at the
hydraulic excitation posts of the simulator, provided by
transducers built into the four-poster, replacing force
measurements as inputs. The applicability of these non-conventional
FRF formulations for modal parameter identification using existing
parameter estimation algorithms is studied. Additionally,
response-only data based on random excitations from the simulator
is processed under the framework of Operational ModalAnalysis
(OMA) for parameter estimation. Modal estimates from these tests
are compared with one another and with those from conventional
EMA-based impact tests, and a summary of results is presented based
on the findings therein.The thesis begins with a general overview
of the automotive testing process, and the role of experimental
modalanalysis and the four-post road simulator therein. Thesis
objectives are presented in terms of utilizing the four-post road
simulator for estimation of the modal parameters of automotive
structures in the absence of force measurements, and the motivation
for the same is discussed. Fundamental principles of experimental
and operational modalanalysis are presented further, in addition
to the theory behind the use of non-force measurements in the
measurement of modified FRFs and consequently the estimation of
modal parameters. The document then proceeds to describe the
experimental setup…
Advisors/Committee Members: Allemang, Randall (Committee Chair).

► As a part of vital infrastructure and transportation network, bridge structures must function safely at all times. Bridges are designed to have a long life…
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▼ As a part of vital infrastructure and transportation network, bridge structures must function safely at all times. Bridges are designed to have a long life span. At any point in time, however, some bridges are aged. The ageing of bridge structures, given the rapidly growing demand of heavy and fast inter-city passages and continuous increase of freight transportation, would require diligence on bridge owners to ensure that the infrastructure is healthy at reasonable cost. In recent decades, a new technique, structural health monitoring (SHM), has emerged to meet this challenge. In this new engineering discipline, structural modal identification and damage detection have formed a vital component. Witnessed by an increasing number of publications is that the change in vibration characteristics is widely and deeply investigated to assess structural damage. Although a number of publications have addressed the feasibility of various methods through experimental verifications, few of them have focused on steel truss bridges. Finding a feasible vibration-based damage indicator for steel truss bridges and solving the difficulties in practical modal identification to support damage detection motivated this research project.
This research was to derive an innovative method to assess structural damage in steel truss bridges. First, it proposed a new damage indicator that relies on optimising the correlation between theoretical and measured modal strain energy. The optimisation is powered by a newly proposed multilayer genetic algorithm. In addition, a selection criterion for damage-sensitive modes has been studied to achieve more efficient and accurate damage detection results. Second, in order to support the proposed damage indicator, the research studied the applications of two state-of-the-art modal identification techniques by considering some practical difficulties: the limited instrumentation, the influence of environmental noise, the difficulties in finite element model updating, and the data selection problem in the output-only modal identification methods.
The numerical (by a planer truss model) and experimental (by a laboratory through truss bridge) verifications have proved the effectiveness and feasibility of the proposed damage detection scheme. The modal strain energy-based indicator was found to be sensitive to the damage in steel truss bridges with incomplete measurement. It has shown the damage indicator's potential in practical applications of steel truss bridges. Lastly, the achievement and limitation of this study, and lessons learnt from the modalanalysis have been summarised.

The present work describes the development and analysis of an experimental apparatus designed to evaluate the contribution of friction materials in vibrations induced on the surface of a brake disc. The proposed apparatus is equipped with a modal exciter (shaker), which was used to promote and control the excitation signal applied in the evaluated friction material. The response of this excitation in the disc surface was measured with accelerometers. The eight samples evaluated in this study was also characterized in terms of its friction coefficient and the asperity distribution of its surface. The modal characteristic of the disc was described in terms of its natural frequencies, damping and modal shapes, whose parameters were obtained by application of experimental modalanalysis. The proposed apparatus was used to identify the main characteristics of the…

► There has been an increasing interest in the field of `smart structures' and `smart materials'. In constructing smart structures, a class of materials called smart…
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▼ There has been an increasing interest in the
field of `smart structures' and `smart materials'. In constructing smart structures, a class of materials called smart materials are often used as sensors and actuators. An example of a smart material is shape memory alloy (SMA). A common actuator configuration uses an SMA wire with a constant load. The non-linear input-output behaviour of SMAs, known as hysteresis, made them difficult to model and control.
The research in this thesis examines the effect of PID-controller gain optimization on SMA wire control at different frequencies of
operation. A constant-load SMA wire actuator with a PID-controller is used in the study. Heat is applied to the wire using an input electric current. The system is cooled through convection with the surrounding area. The lack of active cooling prevents the system from operating at high frequencies.
Three different cost functions are proposed for various applications. The Preisach model is chosen to model the hysteretic behaviour of the SMA wire contraction. Varying material properties such as electrical resistance and heat capacities are modelled to give a more accurate representation of the system's physical behaviour. Simulations show that by optimizing the controller gain values, the bandwidth of the system is improved.
An interesting observation is made in the heating cycle of the SMA wire. In order to achieve faster cooling, overshoot is observed at low frequencies. This is a result of the system hysteresis. The system hysteresis allows different input signals to achieve the same output value. Since the rate of cooling is proportional to the temperature above ambient, better cooling is achieved by reaching a higher temperature. The error caused by the overshoot is compensated by the better cooling phase, which is not actively controlled.

► The error of the production process might come from the structure or generate through the control system. In this study, the model of an arm…
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▼ The error of the production process might come from the structure or generate through the control system. In this study, the model of an arm on double guideway of glue potting dispenser robot is constructed on software the ANSYS 15.0 / Workbench to investigate the impact of the amount of shaking, for the design of arm with different number of holes on it.
Through the simulation, some conclusions had been gotten. For different acceleration and deceleration time the amount of shaking was compared. We found that longer the deceleration time could be effectively reduce the amount of shaking. Different hole destructions by number could not have linear change of shaking. Comparing the natural frequency of the modalanalysis with the vibration frequency, the frequency of 2 holes and 4 holes were very closer for the first order natural frequency. Therefore, the design should exclude the two types of hole distributions. Changing the wall thickness of 6mm, 8mm, 10mm, holes with the thickness of 8mm the amount of rocking was converged faster and the amount of shaking was smaller. The 8 holes and 12 holes of components explored the data from the continuous action of the amount of shaking are more than a single point of movement. They were more than 73% and 75%, respectively.
Advisors/Committee Members: Jung-Hung SUN (chair), C.T.Pan (chair), Chi-Hui-Chien (committee member), T.N.Shiau (chair).

► This thesis mainly focuses on two problems: The first one is to update the modal parameters of linear structures and their associated uncertainties by utilizing…
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▼ This thesis mainly focuses on two problems: The first one is to update the modal parameters of linear structures and their associated uncertainties by utilizing ambient dynamic response data following a Bayesian probabilistic framework. Another issue is how to select the optimal location of sensors. In the first part of this thesis (Chapter 2 - Chapter 4), the problem of identification of the modal parameters of linear structural models using measured ambient response time histories is addressed. Three Bayesian probabilistic frameworks for modal updating are introduced which allow one to obtain not only the optimal values of the updated modal parameters but also their associated uncertainties, calculated from their joint probability distribution. Each of these chapters is corresponding to a different approach. Calculation of the uncertainties of the identified modal parameters is very important if one plans to proceed with a subsequent step of updating the theoretical finite element model based on the modal estimates. These three new approaches will be referred to as Bayesian fast Fourier transform approach (BFFTA), Bayesian spectral density approach (BSDA) and Bayesian Time-domain approach (BTDA). It is found that the updated PDF can be well approximated by a Gaussian distribution centered at the optimal parameters at which the posterior PDF is maximized. Examples using simulated data are presented to illustrate the proposed methods. Another issue addressed in this thesis is for making decisions regarding the optimal location of sensors for modal/model identification. Uncertainties are quantified using probability distributions, and the Bayesian spectral density approach is utilized for deriving appropriate expressions for the updated probability density function (PDF) of the modal/model parameters based on measured ambient response time histories. The optimal sensor configuration is selected as the one that minimizes the information entropy which is a unique measure of the uncertainties in the modal/model parameters. The information entropy measure is also extended to handle large uncertainties expected in the pre-test nominal model of a structure. Genetic algorithms are well-suited for solving the resulting discrete optimization problem. In experimental design, the proposed information entropy can be used to design cost-effective modal/model experiments by comparing and evaluating the benefits from placing additional sensors on the structure in relation to the improvement in the quality of the modal/model parameters identification.

The present study focuses on the popular dynamic reduction methods used in design of complex assemblies (millions of Degrees of Freedom) where numerous iterations are…
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The present study focuses on the popular dynamic reduction methods used in design of complex assemblies (millions of Degrees of Freedom) where numerous iterations are involved to achieve the final design. Aerospace manufacturers such as Rolls Royce and Pratt Whitney are actively seeking techniques that reduce computational time while maintaining accuracy of the models. This involves modalanalysis of components with complex geometries to determine the dynamic behavior due to non-linearity and complicated loading conditions. In such a case the sub-structuring and dynamic reduction techniques prove to be an efficient tool to reduce design cycle time. The components whose designs are finalized can be dynamically reduced to mass and stiffness matrices at the boundary nodes in the assembly. These matrices conserve the dynamics of the component in the assembly, and thus avoid repeated calculations during the analysis runs for design modification of other components. This thesis presents a novel framework in terms of modeling and meshing of any complex structure, in this case an aero-engine casing. In this study the affect of meshing techniques on the run time are highlighted. The modalanalysis is carried out using an extremely fine mesh to ensure all minor details in the structure are captured correctly in the Finite Element (FE) model. This is used as the reference model, to compare against the results of the reduced model. The study also shows the conditions/criteria under which dynamic reduction can be implemented effectively, proving the accuracy of Criag-Bampton (C.B.) method and limitations of Static Condensation. The study highlights the longer runtime needed to produce the reduced matrices of components compared to the overall runtime of the complete unreduced model. Although once the components are reduced, the assembly run is significantly. Hence the decision to use Component Mode Synthesis (CMS) is to be taken judiciously considering the number of iterations that may be required during the design cycle.

► Electric power systems are undergoing significant changes with the deployment of large-scale wind and solar plants connected to the transmission system and small-scale Distributed Energy…
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▼ Electric power systems are undergoing significant changes with the deployment of large-scale wind and solar plants connected to the transmission system and small-scale Distributed Energy Resources (DERs) and microgrids connected to the distribution system, making the latter an active system. A microgrid is a small-scale power system that interconnects renewable and non-renewable generating units such as solar photo-voltaic panels and micro-turbines, storage devices such as batteries and fly wheels, and loads. Typically, it is connected to the distribution feeders via power electronic converters with fast control responses within the micro-seconds. These new developments have prompted growing research activities in stability analysis and control of the transmission and the distribution systems. Unfortunately, these systems are treated as separated entities, limiting the scope of the applicability of the proposed methods to real systems. It is worth stressing that the transmission and distribution systems are interconnected via HV/MV transformers and therefore, are interacting dynamically in a complex way. In this research work, we overcome this problem by investigating the dynamics of the transmission and distribution systems with parallel microgrids as an integrated system . Specifically, we develop a generic model of a microgrid that consists of a DC voltage source connected to an inverter with real and reactive power control and voltage control. We analyze the small-signal stability of the two-area four-machine system with four parallel microgrids connected to the distribution feeders though different impedances. We show that the conventional PQ control of the inverters is insufficient to stabilize the voltage at the point-of-common coupling when the feeder impedances have highly unequal values. To ensure the existence of a stable equilibrium point associated with a sufficient stability margin of the system, we propose a new voltage control implemented as an additional feedback control loop of the conventional inner and outer current control schemes of the inverter. Furthermore, we carry out a modalanalysis of the four-machine system with microgrids using Koopman mode analysis. We reveal the existence of local modes of oscillation of a microgrid against the rest of the system and between parallel microgrids at frequencies that range between 0.1 and 3 Hz. When the control of the microgrid becomes unstable, the frequencies of the oscillation are about 20 Hz. Recall that the Koopman mode analysis is a new technique developed in fluid dynamics and recently introduced in power systems by Suzuki and Mezic. It allows us to carry out small signal and transient stability analysis by processing only measurements, without resorting to any model and without assuming any linearization.
Advisors/Committee Members: Centeno, Virgilio A. (committeechair), Mili, Lamine M. (committeechair), Lai, Jih S. (committee member), Broadwater, Robert P. (committee member), Urken, Arnold (committee member).

Diagne, I. (2017). Dynamic Analysis and Control of Multi-machine Power System with Microgrids: A Koopman Mode Analysis Approach. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/84546

Diagne, Ibrahima. “Dynamic Analysis and Control of Multi-machine Power System with Microgrids: A Koopman Mode Analysis Approach.” 2017. Web. 25 May 2019.

Vancouver:

Diagne I. Dynamic Analysis and Control of Multi-machine Power System with Microgrids: A Koopman Mode Analysis Approach. [Internet] [Doctoral dissertation]. Virginia Tech; 2017. [cited 2019 May 25].
Available from: http://hdl.handle.net/10919/84546.

Council of Science Editors:

Diagne I. Dynamic Analysis and Control of Multi-machine Power System with Microgrids: A Koopman Mode Analysis Approach. [Doctoral Dissertation]. Virginia Tech; 2017. Available from: http://hdl.handle.net/10919/84546

► As we gradually move towards higher penetration of renewable energy sources, the grid must have a safe, feasible, and stable operation at each penetration level.…
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▼ As we gradually move towards higher penetration of renewable energy sources, the grid must have a safe, feasible, and stable operation at each penetration level. For any penetration level throughout this transition, what is a way to identify and install regulation resources such as energy storage devices to effectively damp critical oscillations? Power system planners lack a simple criterion on how to deploy regulation resources and must rely on heavy calculations such as modalanalysis or Prony analysis. This thesis hypothesizes that no matter how complicated the oscillations' behavior and interactions can be, in the case of critical inter-area oscillations, the location to install regulating resources are more importantly related to the system physical characteristics rather than operational characteristics. The focus of this thesis is on the system distribution of inertia in the Western Electricity Coordinating Council (WECC). This goal of this study is to analyze the impact of wind power on the inter-area oscillations WECC system, determine the locations for potential regulation resources, and identify key critical areas for higher wind penetrations.From the analysis of the WECC system, only a few key areas related to machines participating in a given oscillation are viable for a significant improvement through regulation resources. These machines are generally machines in the weaker inertia group of generators. At higher renewable penetrations the machines in the east, southeast, and southwest see higher residue sensitivity index (RSI) values, which means that these areas are more susceptible to active power injections and oscillations in the WECC. The changes in the system with the wind turbine generators (WTGs) highly impact the RSI values, which is due to the topology changes in the system. The RSI does not change significantly for different stable operation points of the system.
Advisors/Committee Members: Hector A. Pulgar, Kai Sun, Kevin L. Tomsovic.

▼ Boundary layer transition for compressible flows remains a challenging and unsolved problem. In the context of high-speed compressible flow, transitional and turbulent boundary-layers produce significantly higher surface heating caused by an increase in skin-friction. The higher heating associated with transitional and turbulent boundary layers drives thermal protection systems (TPS) and mission trajectory bounds. Proper understanding of the mechanisms that drive transition is crucial to the successful design and operation of the next generation spacecraft. Currently, prediction of boundary-layer transition is based on experimental efforts and computational stability analysis. Computational analysis, anchored by experimen- tal correlations, offers an avenue to assess/predict stability at a reduced cost. Classi- cal methods of Linearized Stability Theory (LST) and Parabolized Stability Equations (PSE) have proven to be very useful for simple geometries/base flows. Under certain conditions the assumptions that are inherent to classical methods become invalid and the use of LST/PSE is inaccurate. In these situations, a global approach must be considered. A TriGlobal stability analysis code, Global Mode Analysis in US3D (GMAUS3D), has been developed and implemented into the unstructured solver US3D. A discussion of the methodology and implementation will be presented. Two flow configurations are presented in an effort to validate/verify the approach. First, stability analysis for a subsonic cylinder wake is performed and results compared to literature. Second, a supersonic blunt cone is considered to directly compare LST/PSE analysis and results generated by GMAUS3D.

Brock, J. (2017). Development of Modal Analysis for the Study of Global Modes in High Speed Boundary Layer Flows. (Doctoral Dissertation). University of Minnesota. Retrieved from http://hdl.handle.net/11299/188867

Chicago Manual of Style (16th Edition):

Brock, Joseph. “Development of Modal Analysis for the Study of Global Modes in High Speed Boundary Layer Flows.” 2017. Doctoral Dissertation, University of Minnesota. Accessed May 25, 2019.
http://hdl.handle.net/11299/188867.

MLA Handbook (7th Edition):

Brock, Joseph. “Development of Modal Analysis for the Study of Global Modes in High Speed Boundary Layer Flows.” 2017. Web. 25 May 2019.

Vancouver:

Brock J. Development of Modal Analysis for the Study of Global Modes in High Speed Boundary Layer Flows. [Internet] [Doctoral dissertation]. University of Minnesota; 2017. [cited 2019 May 25].
Available from: http://hdl.handle.net/11299/188867.

Council of Science Editors:

Brock J. Development of Modal Analysis for the Study of Global Modes in High Speed Boundary Layer Flows. [Doctoral Dissertation]. University of Minnesota; 2017. Available from: http://hdl.handle.net/11299/188867

► Viscoelastic coatings are currently being used in a variety of industries to provide shock absorption, energy absorption, noise reduction, and vibration isolation. They are commonly…
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▼ Viscoelastic coatings are currently being used in a
variety of industries to provide shock absorption, energy
absorption, noise reduction, and vibration isolation. They are
commonly used through aerospace, automotive, and electronic
industries. These materials have a complex behavior that causes
their mechanical properties to vary with both temperature and
frequency. Testing historically has been done on a composite
material due to the inability of the coatings to support themselves
at high temperatures. One common method is the vibrating beam
technique, which examines two cantilever beam specimen, an uncoated
beam and a coated beam. The change in modal properties is used to
determine the properties of the viscoelastic material by itself.
However, when the environment is harsh or space is restricted,
measurements and excitations cannot be made in a traditional
contacting manor. This paper examines methods of non-contact
excitation and measurements and explores the effects from these
methods.Specifically, magnetic excitation was examined as a source
of non-contact excitation on a non-ferrous material. This requires
that a magnetic material be attached to the beams in order for the
magnetic excitation to be successful. The mass loading effects were
examined for the two beam specimen to most accurately define the
modal parameters of the beams. This excitation source was also used
to test the specimen at a range of temperatures to determine the
effect temperature had on the modal parameters of the specimen as
well. Finite element models were subsequently created to see if the
results from the experimental modalanalysis could be confirmed
with the FEA results.
Advisors/Committee Members: Allemang, Randall (Committee Chair).

This work represents an investigation of the modalanalysis of distributed parameter systems whose stiffness or…
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▼

Thesis Ph. D. Michigan State University. Mechanical Engineering 2015.

This work represents an investigation of the modalanalysis of distributed parameter systems whose stiffness or damping terms are non-diagonalizable with an undamped modal-coordinate transformation. The non-diagonalizability may be caused by nonmodal damping or stiffness that includes parametric excitation. The modal properties for these kinds of problems will be investigated.An approach for analyzing the complex modes of continuous systems with nonmodal damping is first developed. As an example, a cantilevered beam with damping at the free end is studied. Assumed modes are applied to discretize the eigenvalue problem in state-variable form, to then obtain estimates of the natural frequencies and state-variable modal vectors. The finite-element method is also used to get the mass, stiffness, and damping matrices for the state-variable eigenvalue problem. A comparison between the complex modes and eigenvalues obtained from the assumed-mode analysis and the finite-element analysis shows that the methods produce consistent results. The assumed-mode method is then used to study the effects of the end-damping coefficient on the estimated normal modes and modal damping. Most modes remain underdamped regardless of the end-damping coefficient. There is an optimal end-damping coefficient for vibration decay, which correlates with the maximum modal nonsynchronicity.As an experimental example of a non-modally damped continuous system, an end-damped cantilevered beam is studied for its complex modal behavior. An eddy-current damper is applied considering its noncontact and linear properties. The state-variable modal decomposition method (SVMD) is applied to extract the modes from impact responses. Characteristics of the mode shapes and modal damping are examined for various values of the damping coefficient. The eigenvalues and mode shapes obtained from the experiments are consistent with the numerical analysis of the model, although there is variation relative to sampling parameters. Over the range of damping coefficients studied in the experiments, we observe a maximum damping ratio in the lowest underdamped mode, which correlates with the maximum modal nonsynchronicity. The vibration model of a horizontal-axis wind turbine blade can be approximated as a rotating pretwisted nonsymmetric beam, with damping and gravitational and aeroelastic loading. The out-of-plane (flapwise) and in-plane (edgewise) motion of a wind turbine blade are examined with simple aeroelastic damping effects. Hamilton's principle is applied to derive the in-plane and out-of-plane equations of motion, and the partial differential equation is linearized and then discretized by the assumed-mode method. A simple quasi-steady blade-element airfoil theory is applied to obtain the aeroelastic damping. The analysis is performed on three blades of different size. The effects of nonproportional damping are not strong, but are seen to become more significant as the blade size increases. The…